The invention relates generally to peripheral devices, and more particularly to Universal Serial Bus (USB) devices.
A Universal Serial Bus (USB) compatible peripheral device (e.g., printer, scanner, digital camera, etc.) is attached to a USB host device, such as a personal computer, either directly through a USB interface or through a USB hub. During operation, the host device sends the peripheral device data or command signals. The peripheral device then sends response signals to the host device. For example, a scanner begins to transmit picture data to the host device, a printer outputs a print job or sends an off-line or out-of-paper signal to the host device.
The time that it takes for the host to receive the response signal is called xe2x80x9cturnaround timexe2x80x9d. For the full speed operational mode, the USB protocol provides a maximum of turnaround time of 6.5 USB clock cycles to respond to the host device. If the peripheral device does not respond within the maximum turnaround time period, the host device ignores the peripheral device.
In conventional systems, a substantial component of transmission reception time is used to synchronize the signals from the clock domain of the data rate clock to the clock domain of the application (UTMI) and vice versa. Accordingly it is desirable to reduce the time needed for clock synchronization to maximize the time available for peripheral devices to perform their core function.